From discovery to device: The orbital Hall effect in memory applications

The electron possesses two intrinsic forms of angular momentum: spin and orbital angular momentum. Over the past decade, the spin angular momentum of the electron has been extensively harnessed in spintronic devices, leading to many milestone achievements. In solids, however, the orbital degree of freedom has often been regarded as quenched due to the crystal field effect. Recently, studies leveraging the orbital angular momentum of electrons have unveiled a fascinating discovery: an orbital Hall effect can be observed in materials with weak spin–orbit coupling under an electric field, in which an orbital current can be generated to manipulate the magnetization of ferromagnetic materials and to design novel memory devices. In this review, we summarize key advances in the orbital Hall effect and orbital torque devices. After introducing the physical mechanism of the orbital Hall effect and related phenomena, we highlight orbital torque and associated device concepts. Several challenges facing the development of practical orbital torque devices are then discussed. This review aims to provide a comprehensive overview of the mechanism, detection, and functionalized devices of orbitronics and to explore their potential applications in memory devices, computing components, and terahertz emitters.